1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus to be employed in a facsimile apparatus, a printer, a copy machine and so forth. More specifically, the invention relates to a technology for detecting ejection failure caused by plugging of ejection openings in an ink-jet head or running out of an ink.
2. Description of Related Art
Various systems for performing printing on printing media, such as paper, OHP sheet and so forth have been known. Amongst, an ink-jet printing system is to directly eject an ink toward the printing medium. Such ink-jet system is advantageous in relatively low running cost and low in the level of noise to be generated associated with an operation thereof. On the other hand, in the ink-jet system, it becomes necessary to quickly detect running out of the ink by consuming all of the ink in an ink tank or ejection failure caused by plugging of ejection openings or so forth, to prevent printing failure from occurring, previously.
As an example of a construction for detecting such ejection failure, there has been known a method to perform printing operation of a mark for judgement of presence or absence of the ink on a printing medium, and to make judgement whether the mark is printed or not by means of a reflection type photosensor, in viewpoint of detection of remaining amount of the ink. However, this method requires printing of the mark which is actually unnecessary, only for detecting presence and absence of the ink. Therefore, the printing apparatus employing such method is not user friendly.
In the ink-jet printing apparatus, as a method for detecting faulty condition of ejection, such as running out of the ink, ejection failure due to plugging and so forth, there has been known a technology for passing the ejected ink droplet between a light emitting element and a photo-sensing element of a transmission type photosensor and detecting ejection failure based on whether the light between the elements is interrupted or not.
In one example of construction of the above-mentioned transmission type photosensor, a lens is integrally formed on a light emitting surface of the light emitting element. By this, substantially parallel light is projected toward the photo-sensing element. On the other hand, in a photo-sensing surface of the photo-sensing element, an aperture in the order of 0.7 mm.times.0.7 mm is formed on a light axis by a molding member. By this, in the overall range between photo-sensing and light emitting, detecting range is limited at approximately 0.7 mm in height and approximately 0.7 mm in width. Further, the light emitting element and the photo-sensing element are arranged so that a light axis extending therebetween is in parallel to ejection opening array of the ink-jet head and intersects with a flying path of the ejected ink droplet. Also, a distance between the light emitting element and the photo-sensing element is set to be wider than a range of the ejection opening array. By this, all of the ink droplets ejected from respective ejection openings of the ink-jet head may pass through the detection range between the light emitting element and the photo-sensing element. Thus, when the ink ejection is performed normally and the ink droplet passes the detection range, the ink droplet interrupts the light beam from the light emitting side to reduce the amount of light reaching at the photo-sensing side to cause variation of output of the photo-sensing element. The ejected ink droplet is a fine liquid droplet having a diameter less than or equal to 50 .mu.m. Therefore, normally, a single ink droplet ejected from single ejection opening may not interrupt the light emitted from the light emitting side completely. Instead, light interruption ratio is gradually increased depending upon number of ejection openings ejecting ink. Accordingly, when the output of the transmission type photosensor varies in a magnitude greater than or equal to a given amount, ink ejection is judged as normal. Conversely, when the variation magnitude of the transmission type photosensor is less than or equal to the given amount, failure of ink ejection can be detected.
The above-described technology for detecting ejection failure may perform detection without adding any special parts for the ink-jet head. Therefore, it can be employed as effective means for detection of ejection failure.
When the ejection failure is to be detected in a manner set forth above, it becomes necessary to accurately position a light axis of the photosensor and the ejection opening array of the ink-jet head so that ink ejected from respective ejection openings may cross a light path of the photo sensor. In such case, basically, a shifting magnitude of the ink-jet head from a reference position to the position of the light axis is preliminarily set and positioning is performed by shifting the ink-jet head for the preliminarily set shifting magnitude.
However, due to variations of performance of respective components of a mechanism, which variations are caused when manufacturing the mechanism, for shifting of the head or due to fluctuation in ejection angle of the ink caused by a variation of performing of the ink-jet head, an ink droplet ejected from each ejection opening may be deviated from the light axis of the photosensor in a magnitude of 1 mm at the maximum, even when the positioning operation set forth above is performed. In view of a fact set forth above, the prior art is designed to perform ejection in a range of approximately 2 mm at both sides of the light axis, which range is greater than the range of deviation of the ejected ink droplet, upon detection of the ejection failure. Then, detection of ejection failure is performed by judging whether an output of the photosensor exceeds a predetermined amount when the ejection is performed, or not.
In the prior art as set forth above, since the ink is ejected in the range of approximately 2 mm at both sides of the light axis upon detection of ejection failure, the number of ink droplets to be ejected through each ejection opening becomes about 50 to 100. Therefore, when number of the ejection openings provided in the ink-jet head is, for example, 64, the overall number of the ink droplets to be ejected through respective of the ejection openings becomes about 3200 to 6400 to cause relatively large amount of ink consumption. As a result, the running cost of the ink-jet printing apparatus is raised.
Further, in the case that relatively large tolerance is given for respective components of an ink jet apparatus for lowering of production cost of the ink-jet printing apparatus, the fluctuation in positioning between the light axis and the head becomes further greater so that it becomes necessary to widen the range in which the ejection for detection of the ejection failure needs to be performed. Therefore, ink consuming condition becomes worse.